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Discussion Starter #1
Lately over the past month, i have rough idling problem when my CEL pops up. When it does, my revs flucuate from around 1000-1800, somewhere around there, on top of that, i pulled a code from my obd2 scanner tool and it reads P0113 ( something with IAT circuit/sensor), P0300 random misfire, P0301 ( cylinder 1 misfire), P0304 (cylinder 4 misfire), P0505 (i think it was IAC valve, but that was replaced by the shop recently so i don't think that's an issue unless the valve is clogged). But whenever i drive it for 300 miles, the CEL goes off, then my ECM/PCM (ECU) reverts back the car feeling with no problem except a small rough idle which i think all it takes is cleaning the IACV, but later the CEL will usually go on after 300 more miles. Tonite, i drove my car out heading to the gym and i noticed my CEL came on and when i gas it in any gear then ease off the throttle, my car chuggs somewhat of a shaky feeling even the passenger can feel. BTW, my car is a Honda Civic 99 EX 2DR 5spd transmission. And then i turned off my car for about 5 min then restarted it, it does chugg but have eratic idles as described above. I have the HELMS, Haynes, chilton repair manual, there's several causes. Any help would be appreciated . I couldn't find a thread on this type of problem so i posted it here.
 

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take off your intake. not the manifold. just the intake tubing itself. you'll find 2 holes inside the throttle body. start the car, and plug either of the 2 holes with your finger. if one of them changes your idle in any way, you'll need to do one of the following: 1. either take off your throttle body, and plug up the passage to that hole. (using some silicone or hard plastic, something that will be air tight.) or 2. get a new IACV, probably be easiest to just find a new throttle body at a junk yard.

i had this problem in my old EF, people told me it could have been a number of things, from o2 sensor to idle control valve, to wiring, all kinds of crap. i experimented, and fixed the 1st way. plugged up that passage to the inside of the throttle body. it was used for emissions when the car was made, but being in northern AZ, there's no emissions here. hope this helps.
 

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let me know what happens.
 

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Discussion Starter #5 (Edited)
my car is 0bd2, and doesn't have the FITV valve, i even checked on my repair manual book and it states my type of civic don't have it but it has one hole in the throttle body and i did what you told me to do, plugged my finger in one of the hole and nothing happened to my idle. Other than that any other suggestion would be greatly appreciated! i'll recheck it later again to make sure. i'll keep it updated, so far i've checked the IAT, map sensor circuit, tps to ecu circuit. I'll continue to check all of those emission related component.
 

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well shit man... that's what it was on mine...hope you can figure it out.
 

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If you're getting a misfire, you aren't looking at an IACV problem. Check your rotor, cap, and wires/connections. Then if that isn't looking to fix the problem, check your Knock sensor and it's voltage. Also, you could have a timing issue, injector problem, ECU problem, etc.
 

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If you're getting a misfire, you aren't looking at an IACV problem. Check your rotor, cap, and wires/connections. Then if that isn't looking to fix the problem, check your Knock sensor and it's voltage. Also, you could have a timing issue, injector problem, ECU problem, etc.
oh shit.. i completely overlooked the fast that you were getting misfiring codes.... ^^^he's right. :TU:
 

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Discussion Starter #9
there's no need for me to replace plugs, wires, and rotor, i'm going to check out it with my voltmeter, plus the coil, i doubt that's causing my problem. I did a tuneup on my wires,rotor; plugs were just changed recently As for the injectors, i will check the circuit, if it comes down to checking the injectors for carbon build up, i'll do that and also the fuel pressure. I'm not sure if ECU might be the problem as many people say rarely they go out. I will also check my compression tommorrow, hopefully i can get a vacuum gauge tester and check that too. I have one question, if there's a vacuum leak, will that cause my engine CEL go on? with that possibility will it also make the car misfire? just a thought, i've been checking the repair manual all three of em, the chilton, haynes, helms thoroughly for the possiblity. I've eliminated a few. Defenitely i'll look at the knock sensor hopefully by tommorrow. Thanks guys, i'll keep on updating from what i got.
 

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as far as i know, vacuum doesn't throw a CEL...???
 

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i had the same problem this week but... i ran injector cleaner.. and ran the car pretty hard... seems to run better... *crosses fingers*
 

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I recently did a JDM D15B swap into a 1992 civic 4 door and i used a P28 ECU, after i finished the swap the car ran just like you described and threw a code for IAC so i swaped it out from the one from his old engine and had the same problem , i could get the car to idle fine by unpluging the coolant temp sensor and you would hear like a thump sound from the IAC (it was prolly closing) but it sucks when i do a swap a get a check engine light and it kinda sucks to have to pop the hood evertime the car is cold just to get it to run ok , so i checked the manifold for leaks while it was running with some carb cleaner and there was no leaks that i could find. So on a hunch i went to the honda dealer and got a newfigure 8 O-Ring for the IAC and replaced that , i car has ran fine eversince then , kid has no complaints loves it swap and stage 1 exedy clutch . Hope this will help
 

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Discussion Starter #13
i'm going to run out to autozone/kragens and grab myself those fuel injector cleaner and get the o-ring for the iac, then clean the iac valve and see what happens.
 
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